Desiccant

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A desiccant is a chemical which is hygroscopic enough to absorb water from hydrated compounds in the same sealed environment.

Common desiccants

Comparison

Substance1 pH Water capacity Effectiveness Reversible Notes
Acetonitrile High High Yes Rarely used
Activated alumina Basic or acidic Medium High Yes Can also be used to adsorb fluorides
Activated charcoal Medium Medium Yes Will also adsorb other gasses
Aerogel High High Yes Expensive
Aluminium nitrate Medium Medium No
Bentonite clay
Benzophenone Often used in combination with sodium or potassium
Cadmium nitrate
Calcium High Very high No Reaction with water releases large amounts of hydrogen
Calcium chloride Neutral High Medium Yes Deliquescent; often used in drying tubes
Calcium hydride High Very high No
Calcium nitrate Neutral Medium Medium Yes
Calcium oxide Basic High High No
Calcium sulfate Neutral Low High Yes Very fast and efficient drying agent, but a lot of drying agent might be necessary
Cement (Portland) Alkaline Medium Medium No Used in desiccators, cannot be used directly
Cerium(III) chloride No
Cerium(III) nitrate No
Cesium No Expensive; reaction with water is highly explosive
Cobalt(II) chloride Yes Mostly used as water indicator
Copper(II) sulfate Neutral Low Medium Yes Mostly used as water indicator
Dysprosium(III) chloride No
Dysprosium(III) nitrate No
Erbium(III) chloride No
Erbium(III) nitrate No
Europium(III) chloride No
Europium(III) nitrate No
Gadolinium(III) chloride No
Gadolinium(III) nitrate No
Holmium(III) chloride No
Holmium(III) nitrate No
Lanthanum(III) chloride No
Lanthanum(III) nitrate No
Lithium High High No Expensive; reaction with water releases hydrogen; least violent reaction of all alkaline metals
Lithium bromide Neutral High High Yes
Lithium chloride Neutral Yes Drying must be done in a stream of hydrogen chloride
Luthetium(III) chloride No
Luthetium(III) nitrate No
Magnesium No Reaction is very slow, rarely used
Magnesium sulfate Neutral High Medium Yes Good multipurpose drying agent; exists in powder and granular form; has the ability to absorb a lot of water
Magnesium chloride Neutral High Medium Yes Deliquescent
Molecular sieves High High Yes
Neodymium(III) chloride No
Neodymium(III) nitrate No
Phosphorus pentoxide No
Potassium No More often used to remove traces of water from aprotic solvents
Potassium carbonate Alkaline Low Medium Yes Only for alkaline compounds
Potassium hydroxide Alkaline High High Yes Very effective for basic compounds, such as amines; caustic
Praseodymium(III) chloride No
Praseodymium(III) nitrate No
Rubidium No Expensive; reaction with water is highly explosive
Samarium(III) chloride No
Samarium(III) nitrate No
Silica gel Weak acidic Yes
Sodium No More often used to remove traces of water from aprotic solvents
Sodium hydroxide Alkaline High High Yes Very effective for basic compounds, such as amines; caustic
Sodium oxide No
Sodium sulfate Neutral High Low Yes Used to dry solvents; Requires lots of it; only good for predrying;
Sulfur trioxide High Very high No Tends to form a mist of sulfuric acid in contact with moist air
Sulfuric acid (concentrated) Acidic High High No Used in desiccators, cannot be used to dry solutions directly
Terbium(III) chloride No
Terbium(III) nitrate No
Thulium(III) chloride No
Thulium(III) nitrate No
Ytterbium(III) chloride No
Ytterbium(III) nitrate No
Yttrium(III) chloride No
Yttrium(III) nitrate No
Zinc chloride Acidic Yes Drying must be done in a stream of hydrogen chloride

1All compounds are considered anhydrous.

Gallery

Drying Agents Chart.png